A team at Cornell University working with the Defense Advanced Research Projects Agency (Darpa) has published a report in the journal Nature demonstrating how to hide an event for 40 trillionths of a second.

The effect, described as "spatio-temporal cloaking", depends on the ability to slow the flow of light from events as they occur - making them impossible to observe.

Researchers passed a beam of green light through a lens while travelling inside a fiber-optic cable. The lens split the light into one slow beam and one fast beam, and then fired a red laser into the same space. The red laser was not visible, because it was fired during the gap between the different green lasers.

Confused? We don't blame you. Even the researchers admit there is a big difference between hiding laser beams for 40 picoseconds and hiding military operations lasting minutes - or even several seconds.

According to the team, creating a "time mask" lasting a single second would involve building a machine 18,600 miles long.

"The dispersion of the material is manipulated in time," Nature writes. "Producing a 'time hole' in the probe beam to hide the occurrence of the event from the observer.

"This approach is based on accelerating the front part of a probe light beam and slowing down its rear part to create a well controlled temporal gap - inside which an event occurs - such that the probe beam is not modified in any way."

The implications for the research could still be massive - particularly for military hackers whose data transmissions could be made impossible to detect with similar techniques.